1. Field of the Invention
The present invention relates to a Voice Call Continuity (VCC), and more particularly, to selecting, by a VCC application server or a terminal, a domain by taking into account user preferences and operator policy and placing originating and/or terminating calls over the selected domain.
2. Description of the Background Art
In general, a Voice Call Continuity (VCC) refers to a type of application, namely, a home IMS application which is capable of transporting voice calls between a CS (circuit-switched) domain and an IMS (IP multimedia subsystem) domain. The VCC (also referred to as the VCC application) provides functions of voice call originations, voice call terminations and a domain transfer from the CS domain to the IMS domain or vice versa. Here, the domain transfer refers to transferring access legs for voice calls toward a user equipment (UE) (i.e., a terminal) from the CS domain to the IMS domain or vice versa during an active session. The access leg denotes a call control leg between a VCC UE and a Domain Transfer Function (DTF) of the VCC application.
The domain transfer for a certain voice call/session from the CS domain to the IMS domain or vice versa is performed only when a DTF is positioning on a signal path of the voice call/session setup. For this, positioning of the DTF on the way of the signal path of the voice call/session setup is referred to as anchoring in IMS or anchoring.
FIG. 1 illustrates an architecture of a network for providing a VCC service.
As illustrated in FIG. 1, a VCC UE 10 denotes any type of terminal which support the VCC service. The VCC UE can access CS and PS (packed switched) domains. That is, when accessing the CS domain, the VCC UE uses a UE-CS (not shown) provided therein, whereas a UE-IMS (not shown) provided therein is used when accessing the PS domain.
A VCC application 20 is an application server for providing the VCC service, and is constituted with entities which perform a series of functions. That is, the series of functions may include functions required to setup voice calls toward the VCC UE, and functions required to switch an access leg of the VCC UE between the CS domain and the IMS domain with maintaining an active session. Here, as shown, the series of functions can be a Domain Transfer Function 20a, a Domain Selection Function 20d, a CS Adaptation Function 20b, and a CAMEL Service Application 20c. Detailed capabilities and operations of the series of functions are described in 3GPP TS 23.206 V1.2.0.
Generally, the CS domain entities include Visited Mobile Switching Center (VMSC), Gateway MSC (GMSC), gsmSCF, and the like. The IMS domain entities include P-CSCF, S-CSCF, I-CSCF and Media Gateway Control Function (MGCF). These are known entities.
Hereinafter, a method for processing VCC call origination and VCC call termination in a VCC service will be explained with reference to FIGS. 2 through 5 according to the background art, which is implemented in the network architecture of FIG. 1. FIGS. 2 through 5 illustrate signal paths (or routing) for performing an outgoing/incoming call setup session. That is, FIGS. 2 and 3 illustrate a signal path of an originating call in the VCC service. In particular, FIG. 2 illustrates a signal path of an originating call over a CS domain in the VCC service, while FIG. 3 illustrates a signal path of an originating call over an IMS domain in the VCC service. An originating call is also known as an outgoing call, i.e., a call outgoing from the VCC UE 10 to the VCC application 20. Meanwhile, FIGS. 4 and 5 illustrate a signal path of a terminating call in the VCC service. Particularly, FIG. 4 illustrates a signal path of a terminating call over the CS domain in the VCC service, while FIG. 5 illustrates a signal path of a terminating call over the IMS domain in the VCC service. A terminating call is also known as an incoming call, i.e., a call incoming to the VCC UE 10 terminal from the VCC application 20. Here, the VCC call denotes a call which is terminated or originated by the VCC UE 10, namely, a voice call having a call continuity by being anchored in the VCC application 20 located in the home IMS domain, even while a domain is transferred from the CS domain to the IMS domain or vice versa.
It is assumed in FIGS. 2 through 5 that a user of a UE (i.e., VCC UE) is a VCC subscriber allowing for a home network thus to use the VCC service, and is currently residing in a visited network.
Hereinafter, a signal path of outgoing calls over a CS domain will be explained with reference to FIG. 2 according to the background art.
When a VCC subscriber attempts to place a CS call, the UE which is currently residing in the visited network executes a CS call setup by the VMSC on the CS domain. The CS call is transported over to a Domain Transfer Function (DTF) in the IMS domain of the home network, where it is anchored in the IMS. Next, the session (i.e., the call) corresponding to this is transported over to PSTN, for example, which is a terminating network. Afterwards, normal IMS terminating procedures take place.
Hereinafter, a signal path of outgoing calls over an IMS domain will be explained with reference to FIG. 3 according to the background art.
When a VCC subscriber attempts to place an IMS call, the UE which is currently residing in the visited network executes an IMS call setup on the IMS domain. The IMS call is transported over to P-CSCF via IP-CAN. Afterwards, the IMS call is transported over to the DTF in the IMS domain of a home network, and then transported over to PSTN in a terminating network. Afterwards, normal IMS terminating procedures take place.
Hereinafter, a signal path of incoming calls over a CS domain will be explained with reference to FIG. 4 according to the background art.
When an originating party (or A-party) attempts to place a call to a terminating party (or B-party), the originating party originates a call which reaches a Gateway MSC (GMSC). If the B-party is recognized as a VCC subscriber in the home network, the call is routed to a DTF in the IMS domain. From the DTF, if the call is to be placed over the CS domain, the call is routed back to the CS domain via GMSC, namely, to the VMSC in the visited network. Here, all calls originating from the PSTN to the CS domain are routed to the IMS domain which is thusly anchored in the DTF.
Hereinafter, a signal path of incoming calls over an IMS domain will be explained with reference to FIG. 5 according to the background art.
If an incoming call could be placed to the UE over the IMS domain, the call anchored in the DTF proceeds over to a terminating terminal, namely, to an IMS URI of the UE via the P-CSCF and the IP-CAN of the visited network. That is, the call undergone the same anchoring procedure as illustrated in FIG. 4 is terminated in the IMS domain of the visited network.
Thus, as illustrated in FIGS. 2 and 3, when the UE originates a call (i.e., the call is an outgoing call), the user of the UE (i.e., the VCC subscriber) selects a certain domain (i.e., IMS domain or CS domain) that he prefers to use without taking operator policy into account, and directs the call to the selected domain. Therefore, the background art has technical limitations in that the UE selects a domain without taking the operator policy into account, and directs the call to the selected domain. Here, the operator policy includes information related to the domain selection for calls depending on a current state of a network (e.g., a state regarding resource allocation or traffic, etc.).
Furthermore, as illustrated in FIGS. 4 and 5, the UE can not receive an incoming call over a domain (i.e., IMS domain or CS domain) that he prefers to use. In other words, in the background art, when selecting a domain for an incoming call, a network (i.e., CCCF in detail) selects the domain for an incoming call toward the UE based upon the operator policy without taking into account the UE user's preferences with respect to selecting the domain. Accordingly, the background art contains a technical problem/limitation in that the UE user' preference of a domain selection cannot be or is not taken into account by the VCC application when the VCC application selects a domain in the domain selection process for the incoming call toward the UE.
Therefore, as aforementioned, from the UE perspective, since the UE selects a domain without considering the operator policy which could be changed (or updated) due to, for example, a network state or traffic, etc., there occurs a call inconsistency caused by the traffic of a certain domain (IMS or CS) generated over a network or a lack of resources allocated for a certain domain, or a frequent domain transfer.
Furthermore, from the network perspective, the network (e.g., CCCF) selects a domain without taking into account the user's preferences for selecting a domain of an outgoing call. Accordingly, a call inconsistency occurs or unnecessary domain transfers may be triggered frequently, in case the UE has a mechanical problem or the UE can not be connected to a certain domain.
In addition, the UE user can register or update user preferences through web pages other than the UE. In this case, if the updated preferences are not notified to the network or UE, the domain may incorrectly be selected, which results in a malfunction of the UE.